On alfalfa, the primary symptoms of Peronospora trifoliorum are chlorotic leaf blotches that range from light green to yellow-green to gray-green; rolled or downturned leaves; and thickened, stunted stems ending in rosette-like growths.

Only seedlings and young tissue are susceptible to infection which, with proper cultural controls, can limit the development and progression of the disease.

The disease may overwinter in dead leaf debris, in crown buds, or in seeds[4][5] (UW-Extension, 2006: Pacific Northwest Extension, 2019).

Growing resistant varieties of alfalfa is the most common form of control used against Peronospora trifoliorum[6] (Samac, Rhodes, and Lamp, 2015).

The study found that to some degree, salicylic acid, potassium phosphite, neem oil, Bio-Arec, and Bio-Zaid betaine all protect against downy mildew and numerous other alfalfa diseases[7] (Mohamed Morsy, Fawzy Abdel-Monaim, and Mamoud Mazen, 2011).